- "Different people respond differently to having magic power channeled into them"
Contrary to Voltaire's rudeness in panel four (seriously, Voltaire, rude), these are excellent points to bring up in response to Voltaires vow not to get Elliot killed. People have also brought up additional loopholes that one could use to get around Voltaire's vow and harm Elliot.
And none of them matter. It has been more by virtue of luck than skillful planning that Voltaire has been able to do anything to Elliot at all. While not impossible, the odds of him being able to exploit a loophole and specifically target Elliot with it are low, and up to circumstances and mortals beyond his ability to control.
It's possible he might be a bit miffed about that.